In general, electric vehicles or plug-in hybrid vehicles are equipped with an energy storage device (e.g., a battery) that receives and keeps AC-grid power using a charging facility. Such vehicles are equipped with a charging apparatus that converts AC-grid power provided from an external charging facility into DC power having a desired magnitude in order to charge the energy storage device.
Charging apparatuses that are mounted on vehicles are called On-Board Chargers (OBC) and may include a power factor correction converter that generates DC voltage by correcting the power factor of input AC power and a DC-DC converter that changes the magnitude of output voltage from the power factor correction converter into a magnitude of voltage required for charging a battery. A Y-capacitor is disposed at the input and output terminals of automotive charging apparatuses to remove noise components. In general, the Y-capacitance connected to the output terminal of automotive charging apparatuses is larger in capacitance than the Y-capacitor connected to the input terminal.
The AC power that is provided by charging facilities outside vehicles may be a symmetric type or an asymmetric type, depending on the types of the charging facilities or the types of power supply networks of corresponding countries. When AC power is asymmetric, a common-mode component exists. The common-mode component acts as a low-frequency (grid-power frequency) noise, thereby causing leakage current that leaks to the ground through a Y-capacitor.
In particular, when a DC-DC converter in an automotive charging apparatus is an insulating type including a transformer, the input terminal and the output terminal of the DC-DC converter are isolated to each other, so the common-mode component of grid power does not influence the output terminal of the automotive charging apparatus. However, when the DC-DC converter is a non-insulating type, an electrical connection is formed between the input terminal and the output terminal of the DC-DC converter. Thus, the common-mode component of grid power flows out as low-frequency leakage current through the Y-capacitor connected to the output terminal of the automotive charging apparatus. As described above, since the Y-capacitor connected to the output terminal is very larger in capacitance than the Y-capacitor connected to the input terminal in automotive charging apparatuses, most low-frequency leakage current due to a common-mode concentrates on the Y-capacitor at the output terminal.
An external charging facility includes a Residual Current Detection (RCD) device, but there is a problem that charging is stopped when a low-frequency leakage current over a standard detection level (about 30 mArms) set for RCD is generated.
The description provided above as a related art of the present disclosure is just for helping understanding the background of the present disclosure and should not be construed as being included in the related art known by those skilled in the art.